How can i switch my iCloud account to my iPhone 6

Sign into you Apple ID on your iPhone and make sure you have activated iCloud features in Settings.

Click on this link to learn how to 'Sign in with your Apple ID' --> https://support.apple.com/HT204053

Click on this link to learn how to 'Set up iCloud on your iPhone, iPad, or iPod touch' --> https://support.apple.com/HT208681

Change your iCloud feature settings [iOS and Mac] - https://support.apple.com/HT207689